Congressional investigators have confirmed that a top FBI official met with Democratic Party lawyers to talk about allegations of Donald Trump-Russia collusion weeks before the 2016 election, and before the bureau secured a search warrant targeting Trump's campaign.

Former FBI general counsel James Baker met during the 2016 season with at least one attorney from Perkins Coie, the Democratic National Committee's private law firm.

That's the firm used by the DNC and Hillary Clinton's campaign to secretly pay research firm Fusion GPS and Christopher Steele, a former British intelligence operative, to compile a dossier of uncorroborated raw intelligence alleging Trump and Moscow were colluding to hijack the presidential election.

The dossier, though mostly unverified, was then used by the FBI as the main evidence seeking a Foreign Intelligence Surveillance Act (FISA) warrant targeting the Trump campaign in the final days of the campaign.

The revelation was confirmed both in contemporaneous evidence and testimony secured by a joint investigation by Republicans on the House Judiciary and Government Oversight committees, my source tells me.

It means the FBI had good reason to suspect the dossier was connected to the DNC's main law firm and was the product of a Democratic opposition-research effort to defeat Trump - yet failed to disclose that information to the FISA court in October 2016, when the bureau applied for a FISA warrant to surveil Trump campaign adviser Carter Page.

"This is a bombshell that unequivocally shows the real collusion was between the FBI and Donald Trump's opposition - the DNC, Hillary and a Trump-hating British intel officer - to hijack the election, rather than some conspiracy between Putin and Trump," a knowledgeable source told me.

Baker was interviewed by lawmakers behind closed doors on Wednesday. Sources declined to divulge much about his testimony, other than to say it confirmed other evidence about the contact between the Perkins Coie law firm and the FBI.

The sources said Baker identified lawyer Michael Sussman, a former DOJ lawyer, as the Perkins Coie attorney who reached out to him and said the firm gave him documents and a thumb drive related to Russian interference in the election, hacking and possible Trump connections.

Information gathered separately by another congressional committee indicate the contact occurred in September, the month before the FISA warrant was approved.

A spokeswoman for the FBI declined comment. Spokespersons for Perkins Coie and the Justice Department did not return a message seeking comment.

The sources also said Baker's interview broke new ground both about the FBI's use of news media in 2016 and 2017 to further the Trump case and about Deputy Attorney General Rod Rosenstein's conversations in spring 2017 regarding possible use of a body wire to record Trump.

"The interview was one of the most productive we had and it opened up many new investigative leads," one source said.

Another said Baker could not answer some questions about FBI media contacts, citing an ongoing investigation by the Justice Department inspector general into alleged illegal leaks, during and after the election, about the Trump collusion probe and other matters.

These revelations illustrate anew how much the FBI and Justice Department have withheld from the public about their collaboration and collusion with clearly partisan elements of the Clinton campaign and the DNC, Fusion and Steele, that were trying to defeat Trump.

The growing body of evidence that the FBI used mostly politically-motivated, unverified intelligence from an opponent to justify spying on the GOP nominee's campaign - just weeks before Election Day - has prompted a growing number of Republicans to ask President Trump to declassify the rest of the FBI's main documents in the Russia collusion case.

House Speaker Paul Ryan (R-Wis.), House Freedom Caucus leaders Mark Meadows (R-N.C.) and Jim Jordan (R-Ohio), House Intelligence Committee Chairman Devin Nunes (R-Calif.), veteran investigator Rep. Trey Gowdy (R-S.C.) and many others have urged the president to act on declassification even as FBI and Justice Department have tried to persuade the president to keep documents secret.

Ryan has said he believes the declassification will uncover potential FBI abuses of the FISA process. Jordan said he believes there is strong evidence the bureau misled the FISA court. Nunes has said the FBI intentionally hid exculpatory evidence from the judges.

John Solomon is an award-winning investigative journalist whose work over the years has exposed U.S. and FBI intelligence failures before the Sept. 11 attacks, federal scientists' misuse of foster children and veterans in drug experiments, and numerous cases of political corruption. He is The Hill's executive vice president for video.